Not applicable.
Production material resins are commonly used in the manufacture of a variety of articles including, for example, lightweight interior and exterior parts in automobiles and recreational vehicles such as boat hulls, conversion van parts, truck bed covers, automobile trim and exterior panels, snowmobiles, pull behind campers, motorcycles, and bathtubs. These items are most commonly made from unsaturated polyester resins, which are manufactured and reduced with a solvent monomer containing styrene and other derivatives of styrenated monomers, together with vinyl toluene or methyl methacrylate, to reduce the cost and viscosity of the resin.
Styrene, vinyl toluene, and methyl methacrylate may pose health risks to people exposed to the fumes emitted by these compounds. These materials are also highly flammable, which makes handling and storage of the compounds difficult and expensive. Because of the health hazards associated with exposure to these compounds, these materials are regulated by the Environmental Protection Agency. These monomers typically are included in polyesters at levels of 10% to 90% (w/w), depending on the type of process employed, and on the desired viscosity. Resins made from these materials give off high levels of volatile organic compounds (VOC""s).
Growing concern about environmental, health, and safety issues associated with the use of styrenes in resins has created a demand in the material manufacture industry for nonstyrenated resins that can be used in the manufacture of light weight parts and other articles. To avoid problems associated with the use of styrene in production material resins, nonstyrenated polyester resins have been used in the manufacture of lightweight parts. However, these materials have proven to be unsatisfactory, due to excessive brittleness and poor temperature performance, as evidenced by a low heat distortion temperature (HDT).
What is needed in the art is a nonstyrenated polyester or vinyl ester resin that is suitable for use in the manufacture of light weight parts.
The present invention provides a nonstyrenated polyester, vinyl ester, or dicyclopentadiene (DCPD) resin. In one embodiment, the resin of the present invention comprises a hydroxylated methacrylate monomer and a polymer selected from the group consisting of vinyl esters and DCPD. In a preferred embodiment, the resin comprises a urethane acrylate and a polymer selected from the group consisting of polyesters, vinyl esters, and DCPD. Preferably, the ratio of the weights of monomer and polymer in the resin is in the range of from about 1:9 to 9:1, depending on the properties desired in the resin. Preferably, the monomer is hydroxyethyl methyl methacrylate (HEMA), hydroxyethyl propyl methacrylate (HEPMA), or a hydroxyethyl urethane acrylate.
The nonstyrenated resin of the present invention is characterized by a lack of brittleness and good temperature performance. Preferably, a crosslinked, nonstyrenated polyester urethane acrylate resin has a flex modulus of at least about 250,000 psi, a flexural strength of at least about 8000 psi, and a glass transition temperature of at least about 150xc2x0 F. Preferably, a crosslinked vinyl ester resin has a flex modulus of at least about 900,000 psi, a flexural strength of at least about 20,000 psi, and a glass transition temperature of at least about 450xc2x0 F.
In a preferred embodiment, the resin of the present invention comprises a monomer that is provided as a urethane acrylate. The urethane acrylate used in manufacturing the resin is made by reacting an isocyanate with a methacrylate having a hydroxyl group under suitable reaction conditions well known to those skilled in the art to form a urethane acrylate. Urethane acrylate decreases brittleness in a polyester resin, and enhances impact strength in a vinyl ester resin. Accordingly, in one aspect of the present invention, there is provided a nonstyrenated thermoset resin comprising at least one urethane acrylate monomer and at least one resin selected from the group consisting of polyesters, vinyl esters, and dicyclopentadiene, and combinations thereof, wherein the ratio (w/w) of monomer to resin is between about 1:9 and 9:1 or alternatively wherein the ratio (w/w) of monomer to solid resin is about 3:7 or greater.
Another aspect of the present invention is a method for manufacturing a nonstyrenated polyester or vinyl ester resin comprising the step of reacting a polyester, vinyl ester, or DCPD polymer with a hydroxylated monomer such as HEMA or a urethane acrylate under suitable reaction conditions.
It is an object of the present invention to provide a nonstyrenated polyester, vinyl ester, or DCPD resin that is less brittle and which has a better temperature performance than nonstyrenated polyester resins known to the art.
It is another object of the present invention to provide a method for producing a nonstyrenated polyester or vinyl ester resin that is less brittle and which has a better temperature performance that nonstyrenated polyester resins known to the art.
It is an advantage of the present invention that a polyester or a vinyl ester urethane acrylate resin suitable for use in the manufacture of lightweight parts can be produced without using high levels of volatile organic compounds.
Not applicable.
The present invention includes nonstyrenated polyester, vinyl ester, and DCPD resins that are characterized by lower VOC""s than conventional material resins, and which can be a produced by means that are less deleterious to the environment than methods known to the art. The resins of the present invention are good quality nonstyrenated polyester and vinyl resins that are suitable for use in processes employed in the production of parts or other articles of manufacture.
The present invention also provides a method of making a polyester, vinyl ester, or DCPD resin comprising the steps of: (a) providing at least one monomer selected from the group consisting of hydroxylated methacrylate and urethane acrylate; and mixing at least one monomer of step (a) with at least one liquefied resin selected from the group consisting of an unsaturated polyester, a vinyl ester, and a DCPD resin under suitable reaction conditions. By suitable reaction conditions, it is meant that the polymers are prepared under conditions known to one of skill in the art.
A urethane acrylate for use in the production of the resin of the present invention can be prepared by reacting an isocyanate with a hydroxylated methacrylate such as HEMA or HEPMA to form a urethane acrylate under suitable conditions well-known to one of skill in the art. Urethane acrylates suitable for use in the present invention may be obtained using reaction mixtures comprising HEMA or HEPMA in the range of from about 5% to about 80% and isocyanate in the range of from about 20% to about 95%. One means of obtaining a urethane acrylate suitable for use in the present invention is detailed in the examples below. Briefly, a blocked toluenediisocyanate (TDI) or a straight diphenylmethane diisocynate (MDI) having a percent activate isocyanate groups (NCO%) in the range of from about 1% to about 25% was slowly added to HEMA under agitation. The isocyanate was added gradually over a period of time of at least one hour. The final concentrations of the isocyanate and HEMA were 40% and 60% (w/w), respectively.
The examples below demonstrate the good physical properties of tested resins of the present inventions. A polyester urethane acrylate was formed by mixing the urethane acrylate monomer (50%) with a polypropylene glycol (50%), and a vinyl resin was formed by mixing HEMA (30%) with a vinyl ester (70%) prepared as described below. Other polymers that were used to manufacture resins produced good results, although the complete physical characterization was not conducted. Tested polymers include COR60-169-669-low reactivity orthothalic, COR61-16-670-DCPD, and COR61-169-675 low reactivity DCPD (Interplastics Corporation, Minneapolis, Minn.). It is expected that other ester resins can be used in the present invention, including orthalic, isolthalic, dicyclopentadiene (DPCD), vinyl, epoxyvinyl, novolac vinyl esters, and combinations thereof.
One of skill in the art would be able to select the ratio of the monomer blend to the polyester or vinyl ester polymer employed to achieve certain desired physical properties in the finished product. Increasing the relative percentage of monomer has the effect of lowering Tg, reducing viscosity, increasing tensile properties, lowering flexural properties, and reducing reactivity. Increasing the relative percentage of the ester has the effect of has the opposite effect on these properties.
Other polymers that were tested for use in producing resins include COR60-169-669 Low Reactivity, COR61-169-670-DCPD (Mw=about 2100), and COR61-169-675-Low reactivity DCPD (MW=about 2700) were also used to prepare resins that appeared to have good properties. An increase in the molecular weight of the polyester, DCPD, or vinyl ester decreases its reactivity and produces a more flexible resin. Polymers having a molecular weight in the range of from about 500 to about 7500 are expected to produce resins having desired characteristics.
Optionally, peroxide initiators may be used in the method of the present invention to facilitate curing to obtain a product that is highly cross-linked. Examples of suitable peroxides include cumyl hydrogen peroxide, cumene hydrogen peroxide, methyl ethyl ketone peroxide, acetal acetone peroxide, tertiary butyl perbenzoate, dicumyl peroxide, benzoyl peroxide, cyclohexanol peroxide, or methyl isobutyl ketone peroxide, and combinations thereof. The resins could also be photoinitiated, or catalyzed with anhydrides (a latent epoxy catalyst), or vazo or azo compounds.
The resins produced by the method of the present invention are very versatile and can be used in a number of different processes, including hand lay up, spray chop, resin transfer molding, reaction injection molding, structural reaction injection molding, pultrusion, extrusion, filament winding, bulk molding compound, structural molding compound, cold compression molding, vacuum infusion molding, or rotomolding. These resins are able to withstand autoclaving, which allows the resins to be used for the manufacture of articles that may need to be autoclaved.
In the examples, the resins were melted by means of heat generated by the cutting action created by high shear blades when the mixer was in operation. It is envisioned that a method that achieves melting of the resins by some other means, such as increasing the temperature of the resin by means of an external heat source, could be used in making the resins of the present invention.